Kathmandu, Nepal International SymposiumNovember 20-21, 2014 Geohazards: Science, Engineering and Management

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Paper No. EQ-17

Codal Provisions for Design of Machine Foundations A ReviewBharathi M1, Dhiraj Raj1, Dr. R.N. Dubey2

1Research Scholar, Department of Earthquake Engg., Indian Institute of Technology Roorkee, India2Assistant Professor, Department of Earthquake Engg., Indian Institute of Technology Roorkee, India

Corresponding Author, Email: bharathi.iitr@gmail.com

Key wordsMachine foundation,Code, Design,Recommendations

AbstractMachine foundations are of prior importance in almost all types of industries, asthese are subjected to dynamic loads generated by rotating equipmentsmountedon them. Hence, these should be designed in such a waythat they do not causeany inconvenience during operation. Machine foundations are analyzed anddesigned based on the machine specifications and soil parametersavailable.Theprovisions for the design of machine foundations vary amongcodes/standards of different countries. All the codes/standardsprovide theguidelines forthe design of the foundation and also specify the permissible limitfor displacements to ensure proper functioning of the system. An attempt ismade to review the codes/standards on machine foundations that are availablefor practicing in differentparts of the world. The codes/standards considered forthis study includes ACI 351 3R 04 (America), CP 2012 (British), DIN 4024(German), SAES Q 007 (Saudi Aramco) and IS 2974 (Indian).

1. Machine foundationsDue to tremendous increase in both large and small scale industries, all over the world, theimportance of machine foundation also increases over the time. Engineers fromdifferentbackgrounds are engaged in the analysis, design, construction, maintenance and repair ofmachine foundations. Hence, it is important that the operator, engineers involved from differentspecialization and equipment supplier should collaborate during the design process to make thesystem more efficient and convenient.

2. Considered Codes/standards on Machine FoundationsIn this paper, codes/standards from five different countries are selected for extensive study. Thedifferent types of machines and foundations, design criteria, design methods and constructionconsiderations are elaborated in [1]. Technical terms, materials & methods, designconsiderations for machine foundations and work on site have been discussed by [2]. [3]Describes the flexible structures that support machines with rotating elements, whereas[4]explains about rigid structures that support machines with periodic excitations. Both [3,4]discuss about the basic concepts involved, materials, loads, design and reinforcement

Kathmandu, Nepal International SymposiumNovember 20-21, 2014 Geohazards: Science, Engineering and Management

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detailing.Discussion about the basic definitions, forces, loads, design and drawing of machinefoundation system is available in [10].

The Indian Standardsconsists of five parts which consists of foundation for reciprocatingtype machines [5],foundations for impact type machines (hammer foundations) [6],foundationsfor rotary type machines (medium and high frequency)[7], foundations for rotary type machinesof low frequency[8], and foundations for impact type machines other than hammer (forging andstamping press, pig breaker, elevator and hoist towers) [9]. An overview of all the consideredcodes/standards is presented in the next part.

3. OverviewAll the considered codes/standardsdiscuss the basic terminologies involved in the analysis anddesign of machine foundations. The dynamic soil properties used for the design are discussedalong with the test methods in [1, 2, 10]. The considered loads and their combinations foranalysis are discussed in [1, 10]. Both static and dynamic analysis procedures are elaborated in[1, 3]. Mathematical model of the machine foundation system for simplified analysis with a setof assumptions are described in [3, 6]. A special consideration to steel foundation is given byboth [3, 10]. All the considered codes/standards have depicted the details of reinforcement inthe foundation for better understanding during construction. Design of block and pilefoundation with anti-vibration mounting, workmanship and responsibilities of civil engineeringcontractor, testing and measurement prior to initial running to ensure proper functioning arespecial provisions by [2].

4. Design RecommendationsThe design recommendations by all the considered codes/standards are presented in the form oftables as presented in Table 1. Among them, the Indian Standards have given theirrecommendations for the analysis and design of machine foundations based on the type ofmachine to be mounted on the foundation. Hence, the recommendations by the IndianStandards are represented separately in Table 2.

The recommendations for the analysis and design of both foundation block and pilefoundation have been discussed. Apart from that, the important parameters viz., eccentricity,frequency ratio and limiting amplitude have been compared for the consideredcodes/standards.Both [3,10] are silent about the recommendations for pile foundationssupporting machines; [3] does not specify any eccentricity and limiting amplitude; and [1] issilent regarding frequency ratio.

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Table 1: Recommendations by Considered Codes/Standards other than Indian Standards

Description ACI 351 [1] CP 2012 [2] DIN 4024 [3] SAES Q 007 [10]

2. Foundationblock

Generally thesurface area ofthe foundation isprovided by themanufacturer ofthe machine

Width of foundation thedistance from center ofcrank shaft to the bottom offoundation to ensure thestability against overturning.

The proportion of thefoundation block should besuch as to ensure stabilityagainst rocking.

Mass of foundation = 3 to 5* Mass of the plant

Discussion is available onvarious foundation loads,but not on the geometry.

For simplified verticalvibration, the effect of theground and mass of thefoundation may beneglected for conditionsstated below:

Thickness of the foundation 0.6+ (L/30) inmeter, where L is the length of thefoundation.

Depth of foundation slabs 1/10 of length ofslab.

The foundation must have sufficient width toprevent rocking and adequate depth to permitproperly embedded anchor bolts.

For < 500 HPFoundation weight 3 Machinery weight

For < 200 HPFoundation weight 5 Total machineryweight

For reciprocating machines, a minimum of50% of the block thickness should beembedded in soil.

3.

Lowest naturalfrequency in

case ofLimit

Foundation(rigid) andmachine onspring support

0.80fs

Entire system( rigid) onflexible ground

0.80fs

Foundation asrigid

0.75ff

where, fs is the lowestservice frequencyff is frequency of rigidfoundation on flexibleground

Pilefoundation

It is suggestedthat the block,combined block,table top with orwithout isolators,spring mountedblocks should besupported onpiles in case ofsoft groundconditions wherelow allowablecontact pressureand excessivesettlements areobtained in caseof matfoundation.

The code specifiescircumstances where pilefoundation is required.

Pile cap thickness max(0.6, 1/10 of width)

The mass of soilparticipating with afoundation supported on endbearing piles may beassumed to be the same asfor a raft foundation.

The interaction of closelyspaced friction piles shouldbe considered. Thisinteraction will not be sameas that under static loading.

NA NA

Eccentricity

For, axial andcentrifugalcompressors,with operatingspeed > 25,000rpm, eccentricityof 250 nm.

For compressorsat lower speeds,the maximumallowableeccentricity isdependent onoperating speed.

Plan geometric center offoundation is within 5% ofcenter of mass.

The CG of machine andfoundation system should ifpossible be below the top ofthe foundation block. NA

The horizontal eccentricity, between the CG ofthe machine foundation system and centroid ofsoil contact area 0.05 width or length ofthe foundation.

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Table , ContinuedDescription ACI 351 [1] CP 2012 [2] DIN 4024 [3] SAES Q 007 [10]

FrequencyRatio NA

Important installations:Frequency ratio 0.5 or 2

For less importanceinstallations:Frequency ratio 0.6 or 1.5

When machine is connectedto the foundation by meansof low frequency resilientanti vibration mountings thefrequency ratio > 3.

Further analysis may bedispensed with, if both thefollowing conditions aresatisfied.

First order frequencyLowest natural frequency 0.80fs or 1.25 fs

Higher order frequencyNatural frequency 0.90fs or 1.10fs

For high tuned system:Frequency ratio < 0.7

For low tuned system:Frequency ratio > 1.3

Limitingamplitude

The dynamicforce amplitude isa function ofrotating mass,mass eccentricity,operatingfrequency andservice factor.

To avoiddamage to Limit

NA

If manufacturers vibration criterion is notavailable 0.12 and 0.15 inch per second forcentrifugal and reciprocating machines shall beconsidered as limiting velocity.Machinery

Specified bymanufacturer

Person A chart isproposed

SettlementLow speedmachines200m.

Building

For f < 20Hzits 200m.For f > 20Hza chart isproposed. f =frequency

Others

Only discussionsare available onimportantparametersinvolved sincethis is acommittee report.

Excite the block to samemode of vibration asexpected from operatingmachinery. The vibrationsmeasured by transducerswith linear response over therange 2 to 200 Hz. Theaccuracy of transducersshould be better than 10%and they should respond to auniaxial motion with notmore than 10% crosssensitivity.

Damping factor of theentire system (machineplus foundation) may beassumed to be 0.02 for bothRC and steel structurewhere precise informationis not available.

For fatigue, the dynamic loads shall beincreased by a factor of 1.5.

Any structural component not subjected todynamic forces shall be designed for a quasi-static load of 50% of dead weight of thecomponent in any direction in addition to thestatic design loads.

Transmissibility of amplitudes shall belimited to 20% between adjacent foundations.

For high or low tuned foundations the soilbearing pressures shall not exceed 50% or75% of the allowable bearing pressurespermitted for static loads.

For a system with continuous support, thestiffness of the supporting members of thesteel plate will have 3 times the stiffness ofthe base plate.

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Table 2, Recommendations by Indian Standards

Description IS 2974 [5] IS 2974 [6, 9] IS 2974 [7, 8]

Foundationblock

Empirical rules (related to mass,eccentricity and stability) are suggestedfor deciding the geometry of foundationblock.

Mass of foundation >> Mass of machine

Mass of tup(Tons)

Thickness offoundation block

(m)Dimension

Girdersupporting

Turbine

GirdersupportingGenerator

Up to 1.0 1.00 Clear spanto depth 2 to 3 2.5 to 3.5

1.0 to 2.0 1.25 Depth towidth 1 to 3 1 to 1.5

2.0 to 4.0 1.75 Base Mat

2

Thickness of base raft > 0.07 L4/3, L is theaverage of two adjacent clear span length.(only for raft)

4.0 to 6.0 2.25Over 6.0 2.50

4. Ratio5. Range6. Soil Type7. Mf/ Mt8. 60 9. General10. Mf/ Mt11. 80 to

10012. stiff clay or

compact sandy13. Mf/ Mt14. 100 to

12015. Moderately

firm to softclays andmedium denseto loose sand

16. Where, Mf = Mass of the foundation17. Mt= Mass of the tup

Pilefoundation

Pile caps thickness > 60cm Pile Soil Stiffness factors is obtained by in situ test on single pile with free head condition. In actual practice the pile is used in a

group with pile heads largely restrained by the pile cap. If it is not possible to conduct in-situ tests, computative method ofestimation can be adopted.

The CG of the system (foundation and machine) < 5% length of the foundation with respect to the CG of the pile group. (Applicablefor reciprocating machine only)

Eccentricity

The eccentricity < 5% of the basedimension of block.

CG of combined system should lie belowthe top of the foundation block.

CG of anvil and the foundation block,resultant force in the elastic pad andsupported foundation should coincidewith the line of fall of hammer tup asfar as practically possible.

Under unavoidable circumstance, amaximum eccentricity of 3% basedimension may be allowed.

FrequencyRatio 1.5 <

Kathmandu, Nepal International SymposiumNovember 20-21, 2014 Geohazards: Science, Engineering and Management

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5. ConclusionsAn extensive study about theconsidered codes/standards on machine foundation is carriedoutand a common observation is that the procedure for the design of machine foundationsupported on piles is not available in detail. Some of the considered codes/standards suggestthat the dynamic analysis procedure of piles can be adopted for the analysis and design of pilefoundations supporting machines. This is due to fact that the design of pile foundationssupporting the machines depends on several non-dimensional and interaction parameters.

AcknowledgmentThe authors are grateful to IIT Roorkee for providing the facilities for this investigation.

References1. ACI: 351-3R-2004, "Foundations for Dynamic Equipment", American Concrete

Institute.2. CP: 2012 (Part I)-1974, "Code of practice for Foundations for Machinery",

BSI,London.3. DIN: 4024 (Part I)-1988,"Machine Foundations Flexible Structures that Support

Machines with Rotating Elements", German Standards.4. DIN: 4024 (Part II)-1988,"Machine Foundations Rigid Structures that Support

Machines with Periodic Excitation", German Standards.5. IS: 2974 (Part I)-1982, Code of Practice for Design and Construction of Machine

Foundations - Foundation for Reciprocating Type Machines, BIS New Delhi, India.6. IS: 2974 (Part II)-1980, Code of Practice for Design and Construction of Machine

Foundations - Foundations for Impact Type Machines (Hammer Foundations), BISNew Delhi, India.

7. IS: 2974 (Part III)-1992, Code of Practice for Design and Construction of MachineFoundations - Foundation for Rotary Type Machines (Medium and HighFrequency), BISNew Delhi, India.

8. IS: 2974 (Part IV)-1979, Code of Practice for Design and Construction of MachineFoundations - Foundation for Rotary Type Machines of Low Frequency, BISNewDelhi, India.

9. IS: 2974 (Part V)-1987, Code of Practice for Design and Construction of MachineFoundations - Foundations for Impact Machines other than Hammers, BISNewDelhi, India.

10. SAES: Q007-2003, "Foundations and Supporting Structures for Heavy Machinery",Onshore Structures, Saudi Arabia.